The invention relates to the general field of GMR based magnetic read heads with particular reference to the structure and formation of longitudinal biasing facilities.
As areal recording densities reach several Gbits/in2, development of next generation giant magnetoresistive (GMR) hard disk drive head is under way. In the GMR head design, a GMR read head sensor consists of a sandwich structure: xe2x80x9csensing free layerxe2x80x9d, xe2x80x9cconducting space layerxe2x80x9d, and xe2x80x9cpinned layerxe2x80x9d. The magnetization of the free layer is free to respond to external magnetic field from the media. The magnetization of the pinned layer is pinned at about 90xc2x0 to the magnetization of the free layer. As the conduction electrons are scattered between the free and pinned layers through the spacer, the electrical resistance of the head changes in response to the angle of the directions of magnetization between the free and pinned layers.
In order to obtain a noise-free reproducing waveform, a hard magnetic bias structure is required to suppress the domain walls movement of the free layer. This is accomplished by depositing hard magnetic thin films in an abutting relationship with the free layer on both sides (as seen in plan view). The hard magnetic thin films supply longitudinal magnetic flux to saturate the free layer along its easy axis to a single domain state. The required magnetic flux is approximately the product of remnant magnetization of the free layer and the area of abutting junction. The appearance of the longitudinal bias layer is schematically illustrated in FIG. 1. Seen there is substrate 11 which has been coated with a magnetic shield layer 12 which, in turn, has been coated with dielectric layer 11. Layer 14, which is a cross-sectional view of two parallel stripes (plan view not shown), is a seed layer for the longitudinal bias structure 15. Layer 16 is a separate seed layer (which may or may not be the same as layer 14) upon which the free layer of the GMR structure will later be grown.
Currently, a hard bias layer consists of a 100 xc3x85 Cr underlayer and a CoCr5.2Pt16.2 magnetic layer. The thickness of the CoCr5.2Pt16.2 layer depends on the magnetic flux required to saturate the GMR free layer. This thickness ranges from 350 to 450 xc3x85. Since the GMR head stack is composed of NiFe, CoFe, Cu[FCC (111)], and MnPt[FCT (111 )] layers, a portion of the hard magnetic films formed on the tapered abutting junction on such a crystal structure tends to have its properties greatly deteriorated, particularly its coercive force. In a recent design, a 50 xc3x85 thick Ta seed layer was applied between the Cr underlayer and the abutting junction of the GMR stack. This tantalum layer facilitated growth of Cr BCC (110) over the abutting junction of the GMR stack.
For hard magnetic thin films to be used in a GMR head, three fundamental magnetic properties are required in order to prevent Barkhausen noise (due to domain movement, as mentioned above). First, to ensure that a stable reproducing characteristic is maintained even when an external magnetic field is applied, the hard magnetic thin film must have large coercive force. Second, the in-plane remnant magnetization (Mr) or Mr times thickness Mrt) should be large enough, since this is the component of the hard magnetic thin film that provides the longitudinal bias flux.
If the Mr of the hard magnetic bias layer is less than the Mr of the free layer, with the shared abutting junction, longitudinal bias for the free layer is bound to fall short of supplying the necessary flux. This implies that the saturation magnetization (Ms) and squareness (Mr/Ms) of the hysteresis loop of the hard bias layer along the in-plane direction should be high. Furthermore, the hard bias layer should have high thermal stability to prevent long magnetization decay by thermal activation. With the GMR head shield-to-shield spacing getting closer, we also need to reduce the thickness required in the hard magnetic films by using material with high Ms.
A routine search of the prior art was performed with the following references of interest being found:
The use of longitudinal bias in GMR structures has been disclosed in U.S. Pat. Nos. 5,018,037 and 5,079,035. In U.S. Pat. No. 6,117,570, Chen et al. discuss using CoCrTa layers as a means for increasing the coercivity of CoCrPtTa thin films for use in recording data. They used nickel-aluminum for their seed layer. U.S. Pat. No. 6,020,060 (Yoshida et al.) shows a CoCrTaPt layer while U.S. Pat. No. 5,739,990 (Ravipati et al.), U.S. Pat. No. 5,739,987 (Yuan et al.), U.S. Pat. No. 5,849,422 (Hayashi), U.S. Pat. No. 5,919,581 (Yamamoto et al.), and U.S. Pat. No. 5,919,580(Barnard et al.) all show related patents.
It has been an object of the present invention to provide a hard bias layer with high Ms, squareness (S), high coercivity (Hc), and thermal stability through microstructural engineering.
Another object has been to provide a process for manufacturing said bias layer.
These objects have been achieved by inserting an extra layer between the seed layer and the bias layer. This layer has lattice constants that are intermediate between those of the seed and bias layers thereby improving the crystallinity of the latter. Specifically, a layer of chromium-cobalt-tantalum is inserted between a seed layer of chromium, or chromium-titanium, and a hard magnetic (bias) layer of cobalt-chromium-platinum or cobalt-platinum. About 20 Angstroms is optimum for the thickness of this layer. Data is presented showing that significant improvements in coercivity and hysteresis loop squareness are obtained.